The present invention generally relates to electrography and more particularly, to a toner sealing device or toner scattering prevention device for use in a developing device or a cleaning device of an electrographic copying apparatus and the like.
Generally, prior art electrophotographic copying apparatuses of toner image transfer type have such an inconvenience that, since an opening edge portion of a developing device casing or a cleaning device casing is provided so as to confront a photosensitive or photoreceptor drum (i.e. toner image support member), powdery toner is scattered out of the developing device casing or the cleaning device casing into an apparatus housing, thus resulting in contamination inside the apparatus housing. Accordingly, in the conventional copying apparatuses, it has been so arranged that a base portion of an elastic sealing plate is secured to the opening edge portion of the developing device casing or the cleaning device casing through bonding thereof by the use of a double-coated tape or through depression thereof by the use of a leaf spring, while a tip portion of the elastic sealing plate is brought into light pressing contact with a surface of the photoreceptor drum. However, the known copying apparatuses have such a disadvantage that the elastic sealing plate is inevitably subjected to corrugation or waving during use, thereby resulting in improper sealing of the toner such as scattering of the toner, etc. Namely, the elastic sealing plates of this kind are likely to be subjected to expansion or shrinkage due to environmental changes, aging, etc. Consequently, even if utmost care is taken to prevent formation of corrugations on the elastic sealing plate at the time the elastic sealing plate is secured to the opening edge portion, the sealing plate itself is subjected to expansion or shrinkage due to environmental changes, aging, etc. as described above and thus, the sealing plate is inevitably corrugated at the time of use thereof. For example, in the case where a polyester film measuring 0.05 mm thick, 287 mm long and 20 mm wide is used as the sealing plate, when environmental conditions changed from a temperature of 20.degree. C., and a humidity of 40% r.h. to a temperature of 30.degree. C. and a humidity of 80% r.h., the sealing plate is subjected to an elongation of about 0.18 mm with respect to the length of 287 mm since a coefficient of thermal expansion and a coefficient of moisture swelling of the polyester film are, respectively, 1.5.times.10.sup.-5 cm/ cm/ .degree.C. and 1.2.times.10.sup.-5 cm/ cm/ % r.h.